1. Field of the Invention
The present invention relates to a method of production of a multilayer ceramic capacitor or other multilayer ceramic electronic device.
2. Description of the Related Art
In recent years, as the materials of internal electrode layers of multilayer ceramic capacitors, one type of multilayer ceramic electronic device, it has become possible to use Ni or other inexpensive base materials in place of Pt, Pd, and other expensive precious metals and thereby realize great cost savings.
However, for suitable metallization of the internal electrode layers using a base metal, the green chip has to be fired under a reducing atmosphere. Further, to give the dielectric material reduction resistance for firing under a reducing atmosphere, sometimes Mn is included in the dielectric layers in the green chip before firing. Further, after firing under a reducing atmosphere, to cause reoxidation of the dielectric layers in the sintered body, usually the sintered body is annealed.
Document 1 (Japanese Patent Publication (A) No. 2000-124058) discloses the technology of producing a multilayer ceramic capacitor including internal electrode layers using a base metal by firing together with a reduction resistant dielectric material in a reducing atmosphere, then annealing in a neutral atmosphere with a higher oxygen partial pressure than the firing atmosphere.
Document 2 (Japanese Patent Publication (A) No. 10-163063) discloses technology for controlling the oxygen partial pressure in the treatment atmosphere at the time of the annealing by the CO2 gas or N2 gas and making the holding temperature at the time of annealing 600 to 1100° C. Document 3 (Japanese Patent Publication (A) No. 8-124785) discloses technology for making the holding temperature at the time of annealing 500 to 1100° C. (for example 900° C.) and making the holding time at the holding temperature 9 hours.
That is, in each of the above Patent Documents 1 to 3, after firing the green chip, the obtained sintered body is only annealed.
However, under recent conditions where greater capacity and smaller thickness of the dielectric are being promoted more and the dielectric ratio in recent capacitors is being increasingly reduced, even if optimizing just the annealing conditions, it is difficult to produce capacitors superior in various types of characteristics.
In particular, in conventional technology performing annealing after firing, the IR temperature dependency from room temperature to the high temperature region was good, but the treatment temperature and oxygen partial pressure in the annealing atmosphere could not be suitably controlled and the ends of the internal electrode layers (parts to be electrically connected to the external terminal electrodes) oxidized in some cases. If the ends of the internal electrode layers become oxidized, contact with the external end electrodes formed at the ends of the capacitor body becomes insufficient. As a result, the final product, that is, the capacitor, varies in capacity (capacity variation). End oxidation of the internal electrode layers tended to become worse the thinner and greater the number of the dielectric layers.